This invention relates to electrostatography. The invention relates more particularly to an improved process and apparatus for electrostatography.
In electrostatography an image is reproduced by initially creating an electric charge pattern in image configuration and subsequently utilizing this charge pattern to provide a copy of the image. In one system, the image charge pattern comprises a latent electrostatic charge which is formed on a surface of a photoresponsive body. The latent image is then developed by contacting the surface with a developer material and the developed image is subsequently transferred to a record medium. In another known system, an electric charge pattern is established on pigmented particles which particles are then deposited on a record medium.
In the imaging system wherein a latent electrostatic image is formed on the surface of a photoresponsive body and a developer material contacts the image retention surface, a restriction on processing speed arises as a result of the limited rate at which the developer material can be transported from a source to the surface. This is particularly true with the well known cascade development. Another significant limitation is the relatively weak interaction between the electrostatic latent image and the developer material. This interaction depends upon several factors which in general dictate the use of a relatively thick and correspondingly non-flexible photoreceptor body for the image retention surface. Additionally, separate charging, exposing and developing steps are performed in this imaging process and the performance of these steps is time-consuming and requires relatively expensive and complex apparatus.
Various modifications have been proposed in order to overcome several of these limitations. In U.S. Pat. No. 2,892,709 to E. F. Mayer, the surface of a photoconductor is charged in image configuration through a liquid developer layer while the photoconductor is exposed to a light image. The photoconductor accepts charge in the relatively darker areas thereby forming an electrostatic image on the photoconductor. Toner particles in the liquid developer are drawn to, or precipitate on the surface of the photoconductor in the charged areas thereby forming a visible image. This process is ineffective since it requires the attraction of a charge of one polarity for charging the photoconductor and subsequently requires the attraction of a pigment of an opposite polarity. In another arrangement which is disclosed and claimed in copending U.S. patent application Ser. No. 104,389 filed on Jan. 6, 1971, and which is assigned to the assignee of this invention, an electrophoretic imaging process is provided wherein a suspension of toner particles in an insulating liquid is positioned between a photoconductive electrode and a second electrode. An electric field is established between the electrodes while the photoconductor is exposed to imagewise radiation thereby resulting in an exchange of charge between the photoconductive electrode and toner particles and causing repulsion of the toner particles from the surface of the photoconductive electrode in image configuration. In a further arrangement described in U.S. Pat. No. 2,968,552 to Gundlach which is assigned to the assignee of this invention, particles are deposited on a photoconductive surface and a uniform electrostatic charge is then formed thereon. A transfer medium contacts the charged particles while the particles are exposed through the photoconductive surface in order to provide simultaneous exposure and development.
It is an object of this invention to provide an improved imaging process and apparatus.
Another object of the invention is to provide an improved imaging and in-place development process.
Another object of the invention is to provide an improved imaging process and apparatus which avoids one or more of the above enumerated disadvantages accompanying prior art devices.
Another object of the invention is to provide an electrostatic reproduction process adapted for utilizing a relatively thin photoconductive body.
Another object of the invention is to provide an electrostatic reproduction process of enhanced sensitivity.
Still another object of the invention is to provide an improved electrostatic process adapted for photographic use.
In accordance with the features of this invention, a process for image reproduction comprises the steps of contacting a charge blocking surface on a photoreceptive body with a developer material containing charged toner particles, providing an electric field of predetermined polarity between the photoreceptor and the transfer medium for uniformly attracting the toner particles toward the photoreceptor surface, subjecting the photoreceptor to activating radiation in image configuration for inducing an electrostatic charge pattern in image configuration on the photoreceptor near an interface between the blocking layer and the developer material and providing an electric field of opposite polarity between the photoreceptor and the transfer medium for transferring the toner particles in image configuration to the transfer medium. Automated apparatus and photographic apparatus in accordance with features of the invention are provided.